Orthopedic implant augmentation and stabilization device

ABSTRACT

A prosthesis is provided for replacing a bone surface. The prosthesis includes an implant having a surface for abutting a bone, and an augment configured to be attached to the surface of the implant by bone cement to compensate for bone loss. The augment is formed to include an aperture therein defined by an inner wall. The prosthesis also includes a plastic peg coupled to the implant. The peg is configured to enter the aperture formed in the augment and to engage the inner wall of the augment to retain the augment in a spaced apart relation relative to the implant to permit the implant to be installed onto the bone before the bone cement cures. Alternately, the surface of the implant is formed to include an aperture therein, and a plastic retaining ring located in the aperture formed in the surface of the implant. A metal peg is coupled to the augment. The metal peg is configured to enter the aperture formed in the implant and to engage the plastic retaining ring therein to retain the augment in a spaced apart relation relative to the implant.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to an orthopedic implant augmentation andstabilization device. More particularly, this invention relates to anapparatus which facilitates coupling of an augment to a surface of anorthopedic implant to compensate for bone loss while minimizing surgicaltime and manufacturing costs.

When installing prosthetic implants to replace joints such as in a totalknee replacement operation, it is sometimes necessary to compensate forbone loss which can occur through wear or disease. Bone loss can also becaused by removal of previously installed implants.

It is known to provide spacing wedges or augments to compensate for boneloss and to prevent gaps between the bone and the surfaces of theprosthetic implants installed onto the bone. Current methods which areused to attach augments to the prosthetic implants includes screws,snap-fits, and the use of bone cement. The use of screws to hold theaugments in place on the implant results in metal against metal contact.Micro-motion between the augment and the implant after installation ofthe implant can cause metal fretting particles or metallic debris to beproduced. This can cause an osteolytic reaction and loosening of theimplant. It is also known to provide a snap-fit metal against metalcontact. These snap-fit augments are allowed to wobble in place and canalso produce metal frettings or metallic debris. In addition, it isknown to use metal pegs in combination with bone cement to couple animplant to an augment. However, these known metal pegs also producemetal against metal contact which can cause an osteolytic reaction andloosening of the implant.

It is also known to use bone cement between the augments and theimplant. Current systems that use bone cement to secure the augments inplace do not use anything other than cement to keep the metalliccomponents separated nor do the current systems provide any means forimmediate fixation of the augment to the implant. The components cannotbe implanted until the bone cement between the implant and the augmentis cured. This results in extending the operating room time for thepatient from about 15 minutes to about 45 minutes.

One object of the present invention is to provide an apparatus forattaching augments to implants to compensate for bone loss whileminimizing surgical time, manufacturing costs, and the number ofcomponents necessary to perform surgery.

Another object of the present invention is to provide an apparatus forinitially retaining a metal augment relative to a metal implant withoutproducing any metal against metal contact to permit the implant to beinstalled onto the bone without waiting for bone cement to cure. In thisapparatus, standoff means is provided for separating and positioning themetal augment relative to the metal implant while the bone cement cures,the standoff means comprising plastic means engaging the implant and theaugment.

In one embodiment of the present invention, acrylic pegs or conicalshapes are coupled to the metal implant via ultrasonic welding,interference fits, threads, or other coupling methods. The acryliccomponents can be used along with bone cement to secure and stabilizethe augment relative to the implant. The acrylic components locate andstabilize augments such as tibial and femoral wedges in place until thebone cement between the two components is cured. Therefore, thecomponents of the present invention provide temporary fixation betweenthe augments and the implants until the bone cement cures. The acrylicpegs of the present invention can also provide temporary positioning ofthe implant relative to the bone until the bone cement cures between theimplant and the bone. The acrylic pegs are used to resist movementduring implantation. The acrylic pegs eliminate the metal-to-metalcontact which is present in known devices. In addition, the acrylic pegsof the present invention can be easily cut and aid in removal of thedevice.

In another embodiment of the present invention, metallic pegs orprojections are provided on the augment to increase the ability of thepegs to sustain higher shear loads. In this embodiment, the augments areprovided with an integral square metal peg formed on top of acylindrical boss. The square peg is designed to be interference fit witha plastic sleeve which is fitted into a hole formed in the implant to beaugmented. The cylindrical boss engages the sleeve to provide a standoff to prevent metal against metal contact between the augment and theimplant. The boss region is purposely designed to have a diametersmaller than the outside diameter of the sleeve to ensure that only theplastic sleeve contacts the boss. The square peg permits cement flowpast the flat sides of the peg to eliminate the potential for cementpressure to build up and prevent seating of the augment.

According to one aspect of the present invention, a prosthesis isprovided for replacing a bone surface. The prosthesis includes animplant having a surface for abutting a bone, and an augment configuredto be attached to the surface of the implant by bone cement tocompensate for bone loss. The augment is formed to include an aperturetherein defined by an inner wall. The prosthesis also includes a plasticpeg coupled to the implant. The peg is configured to enter the apertureformed in the augment and to engage the inner wall of the augment toretain the augment in a spaced apart relation relative to the implant topermit the implant to be installed onto the bone before the bone cementcures.

In one illustrated embodiment, the peg includes a generally conicallyshaped head coupled to the surface of the implant and a body portionextending away from the head of the peg. The head portion of the pegengages the inner wall of the augment to retain the augment relative tothe implant.

The body portion of the peg extends through the aperture formed in theaugment beyond a bottom surface of the augment opposite from theimplant. The peg thereby provides means for aligning the prosthesisrelative to the bone.

The prosthesis can include a second plastic peg or standoff meanscoupled to the implant spaced apart from the first plastic peg. Thesecond plastic peg engages a top surface of the augment to provide astand off to maintain the surface of the implant spaced apart from thetop surface of the augment. Such a plastic peg or standoff means may beplaced on the metal augment to engage the metal implant.

In another embodiment of the invention, the implant is formed to includean aperture therein and the peg is press fit into the aperture formed inthe surface of the implant to couple the peg to the implant. The pegincludes first and second conically shaped sections for engaging theimplant and the augment, respectively.

According to another aspect of the invention, a prosthesis is providedfor replacing a bone surface. The prosthesis includes an implant havinga surface for abutting a bone. The surface of the implant is formed toinclude an aperture therein. The prosthesis also includes an augmentconfigured to be attached to the surface of the implant by bone cementto compensate for bone loss, and a plastic retaining ring located in theaperture formed in the surface of the implant. The prosthesis furtherincludes a metal peg coupled to the augment. The peg is configured toenter the aperture formed in the implant and to engage the plasticretaining ring therein to retain the augment in a spaced apart relationrelative to the implant to permit the implant to be installed onto thebone before the bone cement cures.

In this illustrated embodiment, a boss is formed between the peg and theaugment. The boss is configured to engage only a top surface of theplastic retaining ring so that the boss provides a stand off to maintainsaid spaced apart relation between the augment and the implant. The bosshas a generally cylindrical shape. The boss has a predetermined diameterand the plastic retaining ring has a diameter larger than thepredetermined diameter of the boss so that the boss only engages theplastic retaining ring.

A plastic peg may be coupled to the implant spaced apart from theaperture for receiving the metal peg if desired. The plastic peg engagesa surface of the augment to provide a stand off to help maintain theimplant in said spaced apart relation relative to the augment.

Alternately, a plastic peg may be coupled to the augment spaced apartfrom the metal peg if desired. The plastic peg engages a surface of theimplant to provide a stand off to help maintain the implant in saidspaced apart relation relative to the augment.

It is understood that the present invention can be used with tibialcomponents, femoral components, or any other type of implant which mayrequire augments. Additional objects, features, and advantages of theinvention will become apparent to those skilled in the art uponconsideration of the following detailed description of the preferredembodiment exemplifying the best mode of carrying out the invention aspresently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description particularly refers to the accompanying figuresin which:

FIG. 1 is a diagrammatical view of a tibial tray including plastic oracrylic pegs secured to a bottom surface of the tibial tray, and anaugment for attachment to the bottom surface of the tibial tray tocompensate for bone loss;

FIG. 2 is an enlarged fragmentary view illustrating the details of thepeg coupled to the bottom surface of a tibial tray for stabilizing andtemporarily fixing the augment to the tibial tray;

FIG. 3 is a sectional view illustrating another embodiment of thepresent invention in which a peg is press fit into an aperture formed inthe surface of an implant and also press fit into an aperture formed inan augment to temporarily fix the position of the augment relative tothe implant;

FIG. 4 is a sectional view taken through a femoral condyle componentillustrating another embodiment of the augment fixation andstabilization device of the present invention; and

FIG. 5 is a partial sectional view taken along lines 5--5 of FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, FIG. 1 illustrates a tibial prostheticimplant 10 including a stem 12 coupled to a tray 14 in a conventionalmanner. Tray 14 includes a top surface 16 for receiving a conventionalbearing component (not shown) thereon which articulates with a femoralcomponent attached to the resected distal end of the femur. Tibial tray14 also includes a bottom surface 18 which abuts the resected proximalend of the tibia bone. Tibial component 10 is typically made from ametal material.

Bone loss is often present on the resected end of the bone due to wearor disease. Bone loss can also occur upon removal of a previouslyinstalled implant. Therefore, it is often necessary to add metal wedgesor augments 20 to prevent gaps between the bone and the implant. It willbe understood that augments 20 can have any desired shape. Theillustrative augments 20 are formed to include an aperture 21 defined byan inner wall 22. A plastic or acrylic peg 24 is coupled to bottomsurface 18 of tibial tray 14. Illustrative peg 24 includes a truncatedconical head portion 26 having a flat top surface 28 and a generallycylindrical depending body portion 30 coupled to head 26 opposite fromtop surface 28. Top surface 28 of peg 24 may be secured to bottomsurface 18 of tibial tray 14 by ultrasonic welding. It is understoodthat peg 24 can be coupled to tibial tray 14 by any suitable manner suchas by threads or otherwise.

Bone cement 32 is applied between a top surface 34 of augment 20 andbottom surface 18 of tibial tray 14. The bone cement 32 may be aconventional and well known cement used by orthopedic surgeons to attachcomponents to bones. Augment 20 is installed by moving augment 20 indirection of arrow 36 in FIG. 1 until top surface 34 or inner wall 22 ofaugment 20 engages the conical section 26 of peg 24 as illustrated indetail in FIG. 2. Peg 24 provides an interference fit with inner wall 22of augment 20 to retain augment 20 in a spaced apart relation relativeto bottom surface 18 of tibial implant 10 until the bone cement 32between bottom surface 18 of tibial tray 14 and top surface 34 ofaugment 20 cures. Peg 24 prevents the metal augment 20 from coming intocontact with a metal bottom surface 18 of tibial tray 14.

If desired, a second plastic or acrylic peg or standoff means 38 can becoupled to the bottom surface 18 of tibial tray 14 spaced apart from peg24. Second peg 38 may be smaller than the first peg 24 as illustrated.Second peg 38 provides an extra stand off to help prevent metal surface18 from engaging metal surface 34. Any desired number of pegs 24 and 38may be used depending on the application and may be placed on theaugment or the implant.

In the illustrative embodiment, after augment 20 is installed over peg24, a bottom end 40 of peg 24 extends downwardly beyond a bottom surface42 of augment 20. Therefore, the bottom end 40 of peg 24 may preferablyprovide temporary positioning of the implant 10 relative to the boneuntil bone cement between the implant and the bone cures. Duringinstallation, bottom end 40 of peg 24 may be aligned with a holepredrilled into the surface of the bone.

Although the first embodiment illustrated in FIGS. 1 and 2 illustratesthe pegs 24 and 38 attached to the implant 10, it is understood thatpegs 24 and 38 may be coupled to augment 20 instead. In this instance,an aperture for receiving peg 24 would be formed in bottom surface 18 ofimplant 10. The illustrative embodiment of the invention may also beused with any type of implant which requires augmentation.

Another illustrative embodiment of the present invention is illustratedin FIG. 3. In the FIG. 3 embodiment, an implant 50 includes a bottomsurface 52. Bottom surface is formed to include an inner wall 54defining an aperture 55 in the bottom surface 52 of implant 50. Anaugment 56 is designed to be coupled to bottom surface 52 of implant 50.Augment 56 includes a top surface 58 and an inner wall 60 defining anaperture 61 in top surface 58. Bone cement 32 is applied between bottomsurface 52 of implant 50 and top surface 58 of augment 56. A plastic oracrylic peg 62 is press fit into aperture 55 in bottom surface 52 ofimplant 50 until an outer surface of peg 62 engages the inner wall 54 ofimplant 50. Peg 62 includes two conically shaped or tapered sectionsfitting respectively in apertures 55 and 61 to provide the preferredpress fit.

Bone cement 32 is then added to implant surface 52. Augment 56 is theninstalled so that inner wall 60 engages an opposite side outer surfaceof peg 62 to provide an interference fit. Peg 62 provides spacingbetween implant 50 and augment 56 so that surface 52 of metal implant 50does not engage surface 58 of metal augment 56. Peg 62 providestemporary fixation of implant 50 relative to augment 56 until bonecement 32 cures. Implant 50 can be installed onto the bone withoutwaiting for bone cement 32 to cure.

Another embodiment of the present invention is illustrated in FIGS. 4and 5. The embodiment illustrated in FIGS. 4 and 5 is illustrated withrespect to augments for use with a femoral implant. It is understood,however, that this embodiment of the invention can be used with a tibialimplant or any other type of implant in which augmentation is required.

Femoral component 70 illustrated in FIG. 4 includes an anterior surface72, a distal surface 74, and a posterior surface 76. A distal augment 78is provided to add to the distal surface 74 to compensate for bone loss.In addition, a posterior augment 80 is provided to add to the posteriorsurface 76. An anterior augment (not shown) may be provided, ifrequired, to add to anterior surface 72. Implant 70 is illustrativelyformed to include an aperture 82 in distal surface 74 and an aperture 84in posterior surface 76. A retaining sleeve 86 is located in each of theapertures 82 and 84. Retaining sleeves 86 may be made from a PMMA orplastic material.

Augment 78 includes an anterior surface 88, a distal surface 90, and aposterior surface 92. Illustratively, anterior and posterior surfaces 88and 92 are angled at about a 45° angle relative to distal surface 90.Both the bone engaging surfaces of femoral component 70 and the surfacesof augments 78 and 80 have a series of peaks and valleys to increase thesurface area of the implant 70 and augments 78 and 80 for receiving bonecement.

A cylindrical boss 94 having a bottom surface 96 is formed on distalsurface 90 of augment 78 and on posterior surface 81 of augment 80. Asquare metal peg 98 extends away from surface 96 of boss 94. Cylindricalboss 94 has an outer diameter less than the outer diameter of retainingsleeve 86 as illustrated in FIG. 4. Therefore, the metal boss 94 onlyengages the plastic retaining sleeve 86 and not the metal surface ofimplant 70. Bosses 94 provide a standoffs to maintain augments 78 and 80spaced apart from distal surface 74 and posterior surface 76,respectively, of implant 70.

Metal peg 98 is illustratively a square peg designed to have aninterference fit with retaining sleeve 82. Bone cement 32 is placedbetween augment 78 and femoral component 70 to secure augment 78 todistal surface 74 of femoral component 70. Bone cement 32 is also placedbetween posterior surface 82 of augment 80 and posterior surface 76 ofimplant 70 to secure augment 80 to implant 70. The square peg 98 alsopermits cement to flow past the flat slides of the peg to eliminate thepotential for cement pressure to build up inside apertures 82 and 84 andprevent seating of augments 78 and 80, respectively.

As illustrated in FIG. 5, none of the outer boundary edges of augment 78touch the metal surfaces of femoral component 70. The only contactbetween augment 78 and femoral component 70 is between the plasticretaining sleeve 86 and metal boss 94. Metal peg 98 provides temporaryretention of augment 78 and 80 relative to femoral component 70 untilcement 32 cures. Implant 70 can be installed onto the bone before bonecement 32 cures. The metal pegs 98 projecting from augments 78 and 80provide increased strength over the plastic pegs illustrated in FIGS.1-3. Therefore, metal pegs 98 can sustain higher shear loads that may beencountered when seating the implant/augment combination. Metal pegsalso will provide higher resistance to shear loads during use.

Plastic pegs such as those illustrated in FIGS. 1-3 may be used with theembodiment of FIGS. 4 and 5 if required. The plastic pegs (not shown)can be coupled to augments 78 or 80 or to implant 70 to provide extrastand offs to help maintain augments 78 and 80 spaced apart from distalsurface 74 and posterior surface 76, respectively, of implant 70 untilbone cement 32 cures.

Although the invention has been described in detail with reference to acertain illustrative embodiments, variations and modifications existwithin the scope and spirit of the invention as described and defined inthe following claims.

What is claimed is:
 1. A prosthesis for replacing a bone surface, theprosthesis comprising:an implant having a surface for abutting a bone;an augment configured to be attached to the surface of the implant anddisposed between the surface and the bone preventing gaps between thebone and the implant, said augment being attached to the surface by bonecement, the augment being formed to include an aperture therein definedby an inner wall; and a plastic peg coupled to the implant, the pegbeing configured to enter the aperture formed in the augment and toengage the inner wall of the augment to retain the augment in a fixedspaced apart relation relative to the implant to permit the implant tobe installed onto the bone before the bone cement cures.
 2. Theprosthesis of claim 1, wherein the peg includes a generally conicallyshaped head coupled to the surface of the implant and a body portionextending away from the head of the peg.
 3. The prosthesis of claim 2,wherein the body portion of the peg is generally cylindrically shaped.4. The prosthesis of claim 2, wherein the body portion of the peg has agenerally square shaped cross section.
 5. The prosthesis of claim 2,wherein the head portion of the peg engages the inner wall of theaugment to retain the augment relative to the implant.
 6. The prosthesisof claim 2, wherein the body portion of the peg extends through theaperture formed in the augment beyond a bottom surface of the augmentopposite from the implant, the peg thereby providing means for aligningthe prosthesis relative to the bone.
 7. The prosthesis of claim 1,wherein the peg is coupled to the surface of the implant by ultrasonicwelding.
 8. The prosthesis of claim 1, wherein the implant is formed toinclude an aperture therein and the peg is press fit into the apertureformed in the surface of the implant to couple the peg to the implant.9. The prosthesis of claim 8, wherein the peg includes first and secondconically shaped sections for engaging the implant and the augment,respectively.
 10. The prosthesis of claim 1, further comprising a secondplastic peg coupled to the implant spaced apart from the first plasticpeg, the second plastic peg engaging a top surface of the augment toprovide a stand off to maintain the surface of the implant spaced apartfrom the top surface of the augment.
 11. A prosthesis for replacing abone surface, the prosthesis comprising:an implant having a surface forabutting a bone, the implant being formed to include an aperture thereindefined by an inner wall; an augment configured to be attached to thesurface of the implant and disposed between the surface and the bonepreventing gaps between the bone and the implant, said augment beingattached to the surface by bone cement; and a plastic peg coupled to theaugment, the peg being configured to enter the aperture formed in theimplant and to engage the inner wall of the implant to retain theaugment in a fixed spaced apart relation relative to the implant topermit the implant to be installed onto the bone before the bone cementcures.
 12. The prosthesis of claim 11, wherein the peg includes agenerally conically shaped head coupled to the augment and a bodyportion extending away from the head of the peg.
 13. The prosthesis ofclaim 12, wherein the body portion of the peg is generally cylindricallyshaped.
 14. The prosthesis of claim 12, wherein the body portion of thepeg has a generally square shaped cross section.
 15. The prosthesis ofclaim 12, wherein the head portion of the peg engages the inner wall ofthe implant to retain the augment relative to the implant.
 16. Theprosthesis of claim 11, wherein the peg is coupled to a surface of theaugment by ultrasonic welding.
 17. The prosthesis of claim 11, whereinthe augment is formed to include an aperture therein and the peg ispress fit into the aperture formed in the augment to couple the peg tothe implant.
 18. The prosthesis of claim 17, wherein the peg includesfirst and second conically shaped sections for engaging the implant andthe augment, respectively.
 19. The prosthesis of claim 11, furthercomprising a second plastic peg coupled to the augment spaced apart fromthe first plastic peg, the second plastic peg engaging the surface ofthe implant to provide a stand off to maintain the surface of theimplant spaced apart from the top surface of the augment.
 20. Aprosthesis for replacing a bone surface, the prosthesis comprising:ametal implant having a surface for abutting a bone; a metal augmentconfigured to be attached to the surface of the implant and disposedbetween the surface and the bone preventing gaps between the bone andthe implant, said augment being attached to the surface by bone cement;standoff means for separating said metal implants and metal augments andretain said augment in a fixed spaced apart relation relative to saidimplant while the bone cement cures, and standoff means comprisingplastic means engaging said implant and said augment, said plastic meansbeing configured to prevent metal-to-metal contact in said prosthesis.21. The prosthesis of claim 20, in which said standoff means isconfigured as a plastic standoff attached to one of said implant or saidaugment, and the other of said implants or augments is provided with anaperture for receiving said plastic standoff.
 22. The prosthesis ofclaim 20 in which each of said implant or said augment is provided withan aperture for receiving said plastic means.
 23. The prosthesis ofclaim 20 in which said plastic means comprise a plastic ring imbedded inone of said implant or said augment, said standoff means comprising aboss on the other of said implant or said augment, and a peg extendingfrom said boss into said ring.